Fastest way to read and write to/from muliple DAQ channels

[Esmith13]

I'm developing an application in which multiple DAQ channels will be monitored, for example, displacement, load, strain, temperature and so on. My question is what is the fastest and most efficent way to check the value of these inputs, compare them to user inputs and then decide whether or not to write a different voltage to an output. I'm using LV 7.1 on Win 2000.

[LV_Pro]

I guess my first question would be are all these channels going to be on one card? Are you going to just make single measurements (are you interested in instantaneous values vs. "waveforms")? Doing a "Sample channels" for instance will make a single measurement of several channels (on the same board) and present you with an array of the resulting data, one element per channel. How fast do you need to sample, are all of the signals going to be on the same board? The latest NI-Daq allows configuring tasks that mix channel types (T'couples, straight voltage measurements, etc.) which makes configuring the DAQ easier.

If you can give us a little more information regarding what you are trying to accomplish it will help.


P.M.

[Esmith13]

Sorry for such a vague description to start. The channels are going to be read at about 500Hz with instantaneous samples which would then be exported to an Excel file. The output will be writing a single instantaneous value to both analog out channels. All of this is going to the same card (Daq-Pad 6015). The most important function of this program is that it needs to read a value, say displacement, and if this value is out of range write 0 V to the output channels. Except more than one channel needs to be monitored, for example 2 load cells, 2 thermocouples, 2 displacements. If one or some combination of these inputs leaves the specified range the output voltage needs to be turned off as quickly as possible. Thanks for you're help, and let me know if I forgot anymore info.

[Marni]

Hello ESmith.

Thank you for contacting National Instruments. If I understand correctly, you want to collect data from multiple analog input channels and if any of them go out of a range you specify, output a voltage of 0V. Since you have multiple channels you are testing, you will have to do this in software. Use a task to read in your voltages one sample at a time. Use something like Cont Acq&Graph Voltage-Int Clk.vi from the Example Finder (Help Menu>>Find Examples. Browse Hardware Input and Output>>DAQmx>>Analog Measurements>>Voltage.) Create the task in the Measurement and Automation Explorer instead of LabVIEW, so you can have different types of analog measurements in one task. Change the read to read in one sample from multiple channels and create an indicator to view the data. Test the data you collect from the DAQmx Read and use a case structure to output the correct voltage. The less calculations you can make in the while loop, the faster the process. Please let me know if you have any questions. Have a great day!

Marni S.
National Instruments